Technical Field
The present disclosure relates to computed tomography (CT). More particularly, the present disclosure relates to x-ray filters for controlling the spatial intensity distribution of an x-ray beam in CT systems.
Description of Related Art
Computed tomography (CT) systems typically include an x-ray source collimated to form a fan beam directed through an object to be imaged, i.e., a patient, and received by an x-ray detector array. The x-ray source, the fan beam, and the detector array are oriented to be situated within the x-y plane of a Cartesian coordinate system, termed the “imaging plane.” The x-ray source and the detector array may be rotated together on a gantry within the imaging plane, around the imaged object, and hence around the z-axis of the Cartesian coordinate system.
In CT systems, a device called a beam-shaper is generally used to minimize the x-ray radiation dose a patient receives. One of the ways to achieve this goal is to insert a bowtie-shaped piece of polymer, called a “wedge,” in the path of the x-ray beam. The wedge, functioning as an x-ray attenuation filter, is generally a synthetic polymer, such as Teflon having an x-ray absorption spectral characteristic near that of water and hence the human body. The attenuation filter is intended to compensate for the variation in thickness of the imaged body. The x-rays that pass through the center of the imaged body, normally the thickest part, are least attenuated by this filter, whereas the x-rays that pass through the edges of the imaged body, normally the thinnest part, are more attenuated by this filter. The result of this selective attenuation is that the x-rays impinging on the detectors have a similar intensity. The attenuation filter may therefore allow use of more sensitive x-ray detectors reducing the range of x-ray intensities.
An issue with radiology today is how to reduce radiation doses during CT scans without compromising image quality and robustness with respect to patient motion. Therefore, there is an increasing need to develop filters for modulating incoming intensity of an x-ray beam.